Piezoelectric or magnetostrictive actuators for the actuation of fuel injection valves for fuel injection systems of internal combustion engines are usually preloaded by way of a spring in order to eliminate tensile and shear forces. The residual load of the fuel injection valve's return spring, present even when the fuel injection valve is closed, is usually used to generate the preload.
An actuator, e.g., for the actuation of fuel injection valves for fuel injection systems of internal combustion engines, that has multiple layers made of a piezoelectric or magnetostrictive material arranged in stacked fashion, is described in published German patent document DE 199 51 012. The actuator is preloaded by way of a tie rod disposed in a central recess, by an opposite-direction thread. Immobilization and energy transfer are accomplished via a cover plate and a base plate.
This configuration is disadvantageous in particular because of the need to configure the stacked actuator in hollow fashion so that the tie rod can be accommodated in the recess. This makes the actuator even more susceptible to damage during preassembly and assembly.
Described in published international patent document WO 99/08330, is a piezoelectric actuator that is slid into a spring sleeve and joined, in preloaded and in frictionally or positively engaged fashion, to two ends of the spring sleeve. The result is to produce a basic unit in which the preload force of the piezoelectric actuator is permanently defined.
The particular disadvantage of this actuator is that the preload of the actuator is defined solely by the elasticity of the spring sleeve. Progressive characteristics in order to compensate for short activation times cannot thereby be achieved.